Genetic diversity and genealogical relationships among individuals of eight aspen demes in a common garden experiment were studied using microsatellite (SSR) and amplified fragment length polymorphism (AFLP) markers. Moderate to high levels of genetic diversity were observed within all demes for the SSR and AFLP markers. The Shannon index for the AFLP markers was positively and significantly correlated with the average observed heterozygosity for the SSR markers across the demes. Comparative analysis of the numbers of the full-sibling groups inferred by different algorithms suggested that the 2-allele algorithm was more accurate than the other methods used in the study. However, in general, significant correlations were found in the numbers of the full-sibling groups inferred by some other algorithms, such as a heuristic algorithm, the 2-allele algorithm, and the Simpson, modified Simpson and pairwise score algorithms. Among demes, the USA and Swiss demes had the highest and lowest numbers, respectively, of full-sibling groups. This combined approach for sibship reconstruction can also be applied to infer the number of paternal or maternal parents in forest tree plantations when no parental information is available; this approach can improve our understanding of family structure and the extent of genetic diversity within forest tree plantations when no diversity, origin, or parental genotypes information is available.